functionptr.hpp

C++_Templates这本书的随书源码

/* The following code example is taken from the book
 * "C++ Templates - The Complete Guide"
 * by David Vandevoorde and Nicolai M. Josuttis, Addison-Wesley, 2002
 *
 * (C) Copyright David Vandevoorde and Nicolai M. Josuttis 2002.
 * Permission to copy, use, modify, sell and distribute this software
 * is granted provided this copyright notice appears in all copies.
 * This software is provided "as is" without express or implied
 * warranty, and with no claim as to its suitability for any purpose.
 */
#include "forwardparam.hpp"
#include "functionptrt.hpp"

template<typename RT, typename P1 = void, 
                      typename P2 = void,
                      typename P3 = void>
class FunctionPtr {
  private:
    typedef typename FunctionPtrT<RT,P1,P2,P3>::Type FuncPtr;
    // the encapsulated pointer:
    FuncPtr fptr;
  public:
    // to fit in our framework:
    enum { NumParams = FunctionPtrT<RT,P1,P2,P3>::NumParams };
    typedef RT ReturnT;
    typedef P1 Param1T;
    typedef P2 Param2T;
    typedef P3 Param3T;

    // constructor:
    FunctionPtr(FuncPtr ptr)
     : fptr(ptr) {
    }

    // ``function calls'':
    RT operator()() {
        return fptr();
    }
    RT operator()(typename ForwardParamT<P1>::Type a1) {
        return fptr(a1);
    }
    RT operator()(typename ForwardParamT<P1>::Type a1,
                  typename ForwardParamT<P2>::Type a2) {
        return fptr(a1, a2);
    }
    RT operator()(typename ForwardParamT<P1>::Type a1,
                  typename ForwardParamT<P2>::Type a2,
                  typename ForwardParamT<P3>::Type a3) {
        return fptr(a1, a2, a3);
    }
};